Heat-resistant aluminum alloys for electric conductors

ABSTRACT

A HEAT-RESISTANT ALUMINUM ALLOY FOR ELECTRICAL CONDUCTORS WHICH CONSISTS OF 0.01 TO 0.5% (BY WEIGHT, AS NOW AND HEREINAFTER REFERRED TO) ZIRCONIUM, 0.0005 TO 0.08% YTTRIUM AND/OR 0.0003 TO 0.08% ERBIUM AND THE BALANCE OF WHICH IS ESSENTIALLY ALUMINUM.

United States Patent 0.

3,694,195 HEAT-RESISTANT ALUMINUM ALLOYS FOR ELECTRIC CONDUCTORS MinoruYokota, Osaka, Japan, assignor to Sumitomo Electric Industries, Ltd.,Osaka, Japan No Drawing. Filed Oct. 16, 1970, Ser. No. 81,550 Int. Cl.CZZc 21/00 US. Cl. 75-438 5 Claims ABSTRACT OF THE DISCLOSURE Aheat-resistant aluminum alloy for electrical conductors which consistsof 0.01 to 0.5% (by weight, as now and hereinafter referred to)zirconium, 0.0005 to 0.08% yttrium and/or 0.0003 to 0.08% erbium and thebalance of which is essentially aluminum.

BACKGROUND OF THE INVENTION (1) Field of invention This inventionrelates generally to heat-resistant alloys for electric conductors andmore particularly to such conductors which are used as all aluminumalloy conductors (AAAC) and aluminum alloy conductors which are steelreinforced for overhead transmission and distribution lines as well asconductors for other various types of electrical machines andappliances.

(2) Description of the prior art It has been known for some time nowthat aluminumzirconium alloy made by adding a very small quantity ofzirconium to aluminum, may be used with some degree of success as a highresistance and high electrically conductive material for use in electricwires and cables, and in various electric machines and appliances.However, it has been a continuing struggle to provide such aheat-resistant aluminum alloy with ever-improved heat resistancecharacteristics without substantially lowering the electricalconductivity of this aluminurn-zirconium alloy.

With this same object in mind, an attempt at improving the heatresistance characteristics of an aluminumzirconium alloy by adding aquantity of 0.6 to 3.0% of one or two or more of the rare earthelements, chiefly mischmetal, was proposed in US. Pat. No. 3,278,300.That alloy, however, has shortcomings in that although it has anexcellent heat-resistance characteristic at a comparatively lowtemperature range of 100 to 160 C., its properties are not foundsatisfactory at temperatures of 200 to 280 C., which is a temperaturerange that is now beginning to be prescribed for specification tests ofheat-resistance characteristics of materials used in electricalconductors and the like.

SUMMARY OF THE INVENTION It is the principal object of the presentinvention to provide a greatly improved aluminum alloy conductor whichhas a high heat-resistance characteristic without suffering anysubstantial loss in the electrical conductivity of an aluminum-zirconiumalloy by adding thereto a very small quantity of yttrium and/ or erbium.

The heat-resistant aluminum alloy of the present invention consists of0.01 to 0.5% zirconium, at least one element taken from the groupconsisting of 0.0005 to 0.08% yttrium and 0.0003 to 0.08% erbium, andthe balance of which is essentially aluminum.

DESCRIPTION OF THE PREFERRED EMBODIMENT With respect to the use ofyttrium, it is known that the heat-resistance characteristic of aluminumis improved by adding yttrium by itself to aluminum. Compared with thezirconium-containing alloy, however, it has a much lowerheat-resistance, although it has a higher electrical conductivity.

I have continually investigated not only the various components ofmischmetal but also all the other elements as elements to be added forcoexistence with zirconium. As a result, I have discovered that yttriumand erbium in a very small quantity remarkably improve theheat-resistance characteristic without detrimentally affectingelectrical conductivity.

The characteristic of this invention is that the alloy of aluminum andzirconium (0.01 to 0.5 is provided with a very small quantity of yttrium(0.0005 to 0.08%) and/or erbium (0.0003 to 0.08%). That is to say, thisinvention is based on the discovery that unlike ordinary rare earthelements, yttrium and erbium have, because of their high activity, aremarkable effect of improving the heat-resistance characteristicswithout lowering the electrical conductivity when added in a very smallquantity.

The reason why the content of zirconium is prescribed here as 0.01 to0.5% is similar to the reason given with respect to the ordinaryaluminum-zirconium alloy. If the quantity is less than 0.01%, it haslittle effect toward the improvement of heat-resistance characteristics,while if it exceeds 0.5%, its elfect or property to lower the electricalconductivity becomes dominant over its eflfect to improveheat-resistance.

The reason why the content of yttrium is prescribed to be 0.0005 to0.08% is that if the quantity is less than 0.0005, it is scarcelyeffective for the improvement of heatresistance characteristics, whileif it exceeds 0.08%, it not only lowers the electrical conductivity butalso gradually becomes less effective toward the improvement of theheat-resistance characteristics, thereby also becoming disadvantageousfrom the cost viewpoint.

The reason why the content of erbium is prescribed to be 0.0003 to 0.08%is that if the quantity is less than 0.0003%, it is scarcely effectivefor the improvement of the heat-resistance characteristics, while if itexceeds 0.08%, it not only lowers the electrical conductivity but alsogradually becomes less effective for the improvement of theheat-resistance characteristics, thereby also becoming disadvantageousfrom the cost viewpoint.

While the afore-mentioned publicly known invention (US. Pat. No.3,278,300) calls for rare earth elements in a quantity of 0.6 to 3.0%,an addition in a very small quantity is sufficient to attain theobjective if yttrium and/or erbium is used. It is presumed that yttriumand erbium have a qualitatively different effect.

The alloy of this invention may be manufactured by the same casting andworking methods as those for the manufacture of the known aluminumalloys for electric conductors. That is to say, aluminum is melted bythe usual method, desired quantities of zirconium and yttrium and/ orerbium are added thereto, and then cast and worked upon. For instance,aluminum for electrical purposes is melted. A mother alloy ofaluminum-3% zirconium and yttrium and/or erbium are added, melted andcast. It is quite permissible if such usual impurities as, for example,Fe, Si, Mg, Zn, B, V, Ti, Mn, Cr, Cu, Sb, Be, etc., are contained in thealloys of this invention.

This invention will be explained in further detail, referring toexamples (including examples for comparison) set forth hereinafter.

EXAMPLE 1 Aluminum for electric purposes, with the addition of Al-3% Zrmother alloy and yttrium in various combinations, was melted and cast ina metallic mold of 25 mm. in diameter at about 700 C. After hot-rollingof the casting at 500 C. to 19 mm. in diameter, it was drawn by adrawing machine into a Wire rod of 4.0 mm. in diameter. This coldworking is about 95% reduction in area. The electrical and mechanicalproperties of the wire rod obin the eifect on improvement of theheat-resistance characteristic.

Now, using Al-Zr alloy as the base, the dilference in effect between theuse of yttrium as taught by this inventained are shown in Table 1. 5tion and the rare earth elements of the afore-mentioned In this table,the residual value ratio is the ratio obknown invention (U.S. Pat. No.3,278,300), especially tained by dividing the tensile strength afterheating at mischmetal, will be investigated. Since the contents of the280 C. for 1 hour by the tensile strength before heating two aredilferent from the beginning, the content of zirand multiplying theresult by 100. The gauge length for conium is made constant in comparingthem. When the measuring elongation was 250mm. 10 zirconium content is0.04%, the alloys No. 2 to No. 4 of TABLE 1.(n=5) Elec- TensileCompositions (weighttrlcal strength Residual percent analytic value)Eloncondueafter value Tensile gation tlvity heating ratio Num-Mischstrength (per- (per- (kg./ (perber Zr Y metal (kg/mm cent) cent)mm!) cent) 1 0. 04 17.8 2.1 60.9 13.3 74.8 i 3'31 133 3'2 288 ii? '8Aims this 4 I04 17:3 215 60: 9 14 1 7 I2 5 8. 04 17.9 2.6 60.8 14.0 72.76 0.10 18.0 2.7 58.7 16.1 90.6 7 0.10 18.0 2.6 58.6 16.4 91.2 8 0.3018.9 2.9 54.5 18.3 96.8 9 0.04 17.9 2.6 60.7 13.9 77.6 Alloys forcomparison.{ 10 0.10 18.2 2.6 58.5 16.4 90.1 11 0.30 19.0 2.4 54.0 19.195.1 12 0.04 17.8 2.3 60.9 13.1 73.5 13 0.06 17.9 2.4 60.1 14.0 78.1 14o. 10 18.0 2.2 58.7 15.6 86.6 it 3-; 33 3-6 3-3 Alloys 0! Prim 17 III:181 3 21 6 621 1 1214 67: 8 18 21. 1 2. s 60. 6 12. 5 59. 2 19 0.04 17.92.1 60.7 13.1 73.5 20 0. 04 18.1 2.0 60.5 13.3 73.2 21 0.10 18.2 2.158.2 15.7 86.7

1 Each value is a mean value for 5 samples tested.

If the alloys No. 1 to No. 8 of this invention in the this inventionhave a residual value ratio of 76.0%, above Table are compared withalloys No. 9 to No. 11 for 77.0% and 79.2%, respectively (electricalconductivity comparison and alloys No. 12 to No. 21 of prior art, then60.9% while the alloys No. 19 and No. 20 of the prior the effect of thisinvention is evident. art have a ratio of 73.5 and 73.2% respectively(electri- In case the zirconium content is in the neighborhood calConductivity 60.7 and 60.5%). Where the zirconium of 0.04%,theheat-resistance characteristic (residual value content is 0.10%, thealloys No. 6 and No. 7 of this ratio) of the alloys No. 1 to No. 6 ofthis invention is invention have a residual value ratio of 90.6 and91.2% about 75% or more, while that of the alloy No. 12 of therespectively (electrical conductivity 56.7 and 58.6%), prior art is73.5%. It can be seen from this that the heat- While the alloy No. 21 ofthe prior art has a ratio of 86.7% resistance characteristics of thisinventive alloy is greatly (electrical conductivity 58.2% It is thusfound that the improved without scarcely'aifecting the electricalconducalloys of this invention are superior in each case. That is tivity(the electrical conductivity being about 60.9%). By to say, it is notedthat ytrrium in a quantity less than the comparing them with alloy No.13 of the prior art having usual requ red quantity of mischmetal contentis still an increased content of zirconium, the superiority of this moreeffective than mischmetal. inventions alloys with respect to electricalconductivity The alloys for comparison given in Table 1 are Al-Zr-Y maybe understood. alloys such as the alloys of this invention, but havediffer- With aluminum-zirconium alloys of the prior art, there entCOITIPOSItiOII contents. That is to say, the content of werecontradictory trends that if the zirconium content yttrlurn is greaterthan 0.08%. If they are compared on was increased to improve theheat-resistance characterthe h m Of the Same Zirconium Content x pl theistic, it lowers the electrical conductivity. With the alloys alloy No.5 of this invention compared with the alloy No. of this invention,however, it is possible to improve the 9 for comperlson, the alloy 8 Ofs inve tion with heat-resistance characteristic while maintainng theelec- Y 11 p the alloys for tl-ical conductivity constant 60 parisonshow a tendency of having a lower residual value Even when the zirconiumcontent is 0.1%, the same ratloelectllcal Conductivity is naturallyeffect, i.e. an increase in the residual value ratio (im- As 1s clearlyseen from the afore-mentioned examples proved from 86.6% to 91.2% or90.6%), is observed if and the results of their investigating, theaddition of a the alloys No. 6 and No. 7 of this invention are comparedvery small quantity of yttrium to aluminum-zirconium with the' alloy No.14 of the prior art. When the zirconium alloys according to thisinvention greatly improves the content is in the neighborhood of 0.30%,the elfect on heat-resistance characteristic without substantiallyatfectboth electrical conductivity and the heat-resistance charingelectrical conductivity. acteristic is observed if th alloy No. 8 ofthis invention is compared with the alloy No. 15 of the prior art.EXAMPLE 2 Next, comparison will be made with an aluminumyttrium alloywhich is one of the alloys known in the prior The mother alloy of A1370Zr and a Very Small q art. The residual value ratio of the alloys No. lto No. 5 my of erbium were added to aluminum for electric P of thisinvention is 74 to 79% (electrical conductivity poses in variouscombinations, and melted and cast in a 609% hil th t f th alloys N 16 tNo 18 f the metallic mold of 25 mm. in diameter. The conditions priorart is 59 to 67% (electrical conductivity 60 to 75 under which thesamples were prepared and measurements 62%), from this, a difference maybe distinctly observed were made are the same as in the case of theafore-mentioned Example 1. The results obtained are shown in Table 2.

TABLE 2.(n=5) tion have a residual value ratio of 90.2 and 90.5respectively (electrical conductivity 58.7 and 58.6%), while theCompositions weight percent analytic Elec- Tensile Residvalue) TensileElontrical strength ual value N umstrength gation conducafter ratio berZr Er (kg/mm!) (pervity heating (percent) (percent) (kg/mm!) cent) 22 0.04 0. 0005 18. 2. 4 60. 9 13. 6 75. 23 0. 04 0. 003 18. 1 2. 6 60.9 14.0 77. 2 24 0. 04 0. 009 17. 9 2. 4 60. 9 14. 3 80. 0 Alloys of thisinvention. 25 0. 04 l8. 2 2. 6 60. 8 14. 0 77. 0 26 0. 0. 004 18. 2 2. 468. 7 16. 4 90. 2 27 0. 10 0. 04 18. 1 2. 7 58. 6 16. 4 90. 5 28 0. 310. 03 18. 9 2. 8 54. 5 18. 4 97. 2 29 0. 04 0. 10 18. 1 2. 3 60. 5 13. 976. 7 Alloys for oomparisom"; 80 0. l0 0. 10 18. 3 2. 6 58. 4 16. 4 89.5 31 0. 30 0. 19 19. l 2. 6 64. 0 18. 0 94. 2

1 Each value is a value for 6 samples tested.

The efiect is obvious if the alloys No. 22 to No. 28 of this inventionshown in the above table are compared with the alloys No. 29 to No. 30'for comparison and with the alloys No. 12 to No. 18 of the prior artshown in Example 1.

When the content of zirconium is in the neighborhood of 0.04%, thealloys No. 22 to No. 25 of this invention have a heat-resistance(residual value ratio) of about 77% or more, while the alloy No. 12 ofthe prior art shows a value of 73.6%. From this it can be seen that theheatresistance characteristic is markedly improved without hardlyafiecting the electrical conductivity (electrical conductivity about60.9%) at all. If comparison is made with the alloy N0. 13 of the priorart which has an increased zirconium content, it will be understood thatthis invention is favorable with respect to electrical conductivity.

That is to say, in the case of the aluminum-zirconium alloy of the priorart there is a contradictory tendency that if the zirconium content isincreased to improve the heat-resistance characteristic, it results in adecrease in electrical conductivity. If the alloys of this invention areused, however, it is possible to improve the heat-resistancecharacteristic while maintaining electrical conductivity constant.

Also, where the zirconium content is 0.1%, the same effect, namely anincrease in the residual value ratio (improved from 86.6% to 90.2% or90.5% can be observed if the alloys No. 26 and No. 27 of this inventionare compared with the alloy No. 14 of the prior art. When the zirconiumcontent is in the neighborhood of 0.30%, the effect On both electricalconductivity and the heat-resistance characteristic is observed bycomparing the alloy No. 28 of this invention with the alloy No. of theprior art.

Now, using Al-Zr alloy as the base, the difference in alloy No. 21 ofthe prior art has a ratio of 86.7% (electrical conductivity 86.2%). Fromthese examples, it can be seen that the alloy of this invention issuperior in each case. That is to say, it is observed that erbium, in aquantity less than the usual required quantity of mischmetal, is moreeifective than mischmetal.

The alloys for comparison in the above table are Al-Zr-Er alloys such asthe alloys of this invention, but have different composition contents.They are given an erbium content which exceeds 0.08%. If they arecompared when the zirconium content is the same amount (for example, thealloy No. 25 of this invention compared with the alloy No. 29 forcomparison, and the alloy No. 27 of this invention with the alloy No. 30for comparison), the alloys for comparison show a tendency toward adecrease in the residual value ratio. (Naturally they have :a lowerelectrical conductivity.)

As can be clearly seen from the afore-mentioned examples and the resultsof their investigation, the addition of a very small quantity of erbiumto aluminum-zirconium alloy according to this invention greatly improvesthe heat-resistance characteristic without hardly alfecting electricalconductivity at all.

EXAMPLE 3 Aluminum for electrical purposes with additions of Al-3% Zrmother alloy, erbium and yttrium in various combinations of quantities,was melted and cast in a metallic mold of 25 mm. in diameter. Theconditions under which samples were prepared and measurements were madeare the same as in the case of Example 1. Some of the results obtainedare shown in the table below.

TABLE 3.(n=5) 1 Compositions (weight Elee- Tensile percent, analytictrical strength Residual value) Tensile Elonconducafter value strengthgation tivity heating ratio Nnm- (kg. (per- (per- (kg. (perber Zr Y Ermmfl) cent) cent) mmfl) cent) 31 0. 04 0. 01 0. 002 18. 1 2. 6 60. 9 14.4 79. 5 Alloys of this invention. 32 0. 04 0. 001 0.011 18. 2 2. 3 60. 914. 7 80. 9 33 0. 10 0. 01 0. 01 18. 3 2. 6 58. 7 16. 5 90. 5

1 Each value is a mean value for 5 samples tested.

effect between the use of erbium in accordance with this invention andrare earth elements, mischmetal, of the afore-mentioned known invention(US. Pat No. 3,278,300) will be investigated. Because the quantitiescontained are different from the beginning, the quantity of zirconiumcontained is made constant for comparison. When the zirconium content is0.04%, the alloys No. 22 to No. 24 of this invention have a residualvalue ratio of 75.5, 77.2 and 80.0%, respectively (electricalconductivity 60.9%), while the alloys No. 19 and No. 20 of the prior arthave a ratio of 73.5 and 73.2% respectively (electrical conductivity60.7 and 60.5%). When the zirconium content is 0.10%, the alloys No. 26and No. 27 of this inven- If the alloys No. 31 to No. 33 of thisinvention are compared with the alloys No. 12 and No. 14 of the priorart given in Example 1, it can be seen that a very small quantity ofyttrium and erbium greatly improves the heat-resistance characteristicwithout affecting electrical conductivity.

The reason why only yttrium and erbium, among various mischmetals, havesuch a great effect is not completely understood. But it is consideredthat the mechanism for the efiect may be that the very small quantity ofyttrium and/or erbium in aluminum help the heatresistance elfect of thezirconium addition as a result of combining with voids or the like foundtherein.

7 I claim: 1. A heat-resistant aluminum alloy for electric conductorsconsisting of 0.01 to 0.5% zirconium, at least one element selected fromthe group consisting of 0.0005

to 0.08% yttrium and 0.0003 to 0.08% erbium, and the balance of which isessentially aluminum.

2. A heat-resistant aluminum alloy for electric conductors whichconsists of 0.01 to 0.5% zirconium, 0.0005 to 0.08% yttrium and thebalance of which is essentially aluminum. I

3. A heat-resistant aluminum alloy for electric conductors whichconsists of 0.01 to 0.5 zirconium, 0.0003 to 0.08% erbium and thebalance of which is essentially aluminum.

4. A heat-resistant aluminum alloy for electric conductors whichconsists of 0.01 to 0.5% zirconium, 0.0005 to 0.08% yttrium, 0.0003 to0.08% erbium and the balance of which is essentially aluminum.

5. A high heat-resistant aluminum alloy for electrical conductors havingan improved heat resistance characteristic satisfactory at temperaturesof 200 C. to 280 C. without detrimentally effecting the electricalconductivity consisting of a zirconium-aluminum containing 0.01 to 0.5zirconium to which is added at least one element selected from the groupconsisting of 0.0005 to 0.08% yttrium and 0.0003 to 0.08% erbium.

References Cited UNITED STATES PATENTS 3,278,300 10/1966 Koike 75138RICHARD O. DEAN, Primary Examiner US. Cl. X.R.

Patent No. 3, 94,195 I Dated s m 25 13 Invent r( Minoru Yokota It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Col. 1, between lines 6 and 7, insert the following:

-- Claims priority, application Japan October 24, 1969 84650/1969;January 31, 1970 8755/1970-- Signed and sealed this 22nd day of May1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents FORM FO-1050 (1 USCOMM-DC scan-ps9 9 U. 5. GOVERNMENTPRINTING OFFICE: I969 0-366-334

